@Mary-Lisa1 While it is sad that the guest was potentially in a car accident (if this is even true given her history of dramatic storytelling), these are circumstances beyond your control and where things like travel insurance should come into play. At the end of the day whether we have 100 properties or rent a room in our home, Airbnb is a business that provides us some level of financial support.
In all honesty I think you have been more than accommodating by allowing her to make alterations FIVE times. These alterations ultimately affect your calendar and availability. Additionally, one dramatic story, maybe two, is believable, but six is reaching. I would be willing to bet the car accident was fabricated or embellished to some degree.
At the end of the day, a car accident is not considered an extenuating circumstance, and you have no obligation to refund her. Personally, speaking I would not. I would however ask her to cancel and offer her an additional refund should the dates be able to be rebooked. I would say something to the following degree:
"Hello (Insert guest name) I am sorry to hear about your accident and hope you recover swiftly. Unfortunately, given that your reservation is in less than two weeks, it would not be feasible for me to go outside my cancellation policy and offer a full refund, as the dates are not likely to be re-booked. I do however encourage guest who cannot fulfill their reservation to cancel, so the dates become available to other potential guest. In the event I re-book any of those days, I will offer you an additional refund. "